1. Field of the Invention
This invention relates to a method and an apparatus for the generation of a spiral gas stream in a pipeline, and methods and apparatus for the utilization of the spiral gas stream thus generated for the transportation of solid particles and for other purposes.
2. Description of the Prior Art
It has been widely applied for a long time in industry to transport particles of various solids, including coal, ore and cement, by gas stream in pipeline.
The fundamental principle of this transportation method is very simple: Pressurized gas is fed into a pipeline to form a high-speed gas stream, in which solid particles are suspended and transported to the outlet of the pipeline. To avoid the sedimentation of solid particles which cause the blockade of the pipeline on the midway, it is inevitable to keep the velocity of gas stream in the pipeline at high level. In general, solid particles of larger size and higher specific gravity require the higher velocity of gas stream.
Consequently, the gas pressure at the inlet of the pipeline should be higher as the size and the specific gravity of the solid particles as well as the length of the pipeline increase. The gas pressure applied to high pressure pneumatic transportation system ranges usually from 2 to 7 Kg/cm.sup.2 G.
Several points have been raised in this conventional transportation system. The first point consists in a fact that a feeder for supplying solid particles into the pipeline is exposed to high gas pressure.
Usually, a screw conveyor functions as such a feeder as this, especially because a screw conveyor makes it easy to control quantitatively the amount of solid particles to be supplied, but from the structural point of view, a screw conveyor is deficient in gas sealing properly. Pressurized gas at the inlet of the pipeline can blow back in the screw conveyor to form voids in the solid particles there. Not only such voids lower the conveyor's supply efficiency and make it difficult to control quantitatively the amount of solid particles to be supplied, but also the blow backed fine solid particles enter into the bearings of rotating part in the conveyor to wear rapidly the shafts and bearings. In addition, the hopper for feeding solid particles to the screw conveyor must be also air-tight. Consequently, when such a hopper becomes empty, it is necessary to interrupt the transportation of solid particles for the purpose of recharging it or to change over to another hopper.
To eliminate such difficulties as mentioned above, several devices for preventing possible blow back of gas by means of improved structure of a screw conveyor have been proposed in U.S. Pat. Nos. 3,602,552 and 3,975,058 etc., but as a result the structure becomes at any rate complicated.
The second point in the conventional transportation system of solid particles with high-speed gas stream in a pipeline is wear of the inside wall of the pipeline due to collision of solid particles. When the velocity of gas stream is sufficient to transport solid particles of high specific gravity, the gas stream in pipeline forms a turbulent flow, and the solid particles suspended in this violently collide against the inside wall of the pipeline also under turbulent condition, and if the solid particles are highly hard, the particles will wear the inside wall of the pipeline as if sandblasting does and finally piece the pipe wall. This phenomenon is remarkable especially in the bend zones of pipeline.
Since this problem is not yet effectively solved, it is inevitable to repair or exchange for new parts with such a high frequency as once a month for the bend zones of pipeline transporting pneumatically such highly hard solid particles as ore.